As illustrated in FIG. 1, an aircraft engine 1 habitually includes a low-pressure compressor 2 fitted with a compressor shaft 3 surrounded by a fan casing 4 and an intermediate casing 5. Fan casing 4 in particular retains fan blades 6 and also fragments of fan blade 6. When a foreign body comes into collision with a fan blade 6 it can be damaged. When such damage occurs blade fragments can be detached from rotating blade 6 and, under a centrifugation effect, be displaced such that they are in contact with the inner surface of fan casing 4. Such damage can also be due to vibratory phenomena.
More specifically, as illustrated in FIG. 2, this type of fan casing 4 habitually has three separate parts 7, 8, 9, which are dimensioned so as to contain each blade fragment in the event of loss of blade 6. When blade 6 is lost the upstream portion 7 and downstream portion 9, which are less thick, respectively contain the blade tip and the blade root whereas central portion 8 (called the containment portion) enables the higher-energy blade fragments, which have been displaced under centrifugal forces, to be contained. Thus, during the lifetime of an aircraft engine 1 damage of the impact type appears on fan blade 4, and it is must be guaranteed that it can resist such damage. With the aim of improving the lifetime of fan casing 4 it is possible to use fan casings 4 with a thicker containment area.
But since this thickening started to be applied in 2013 the majority of aircraft engines 1 sold before this time do not have such thickening. Consequently, a large quantity of casings 4 are out of service after damage has been observed. Such thickening also increases the total mass of the aircraft fitted with this fan casing, and consequently increases fuel consumption.